In the prior art, tomography techniques reconstructing an original three-dimensional figure of an object from images of the object captured in multiple imaging directions have been proposed.
For example, in the CT (computer tomography) scan known as a medical technique, a radiation source and a detector are placed with an object in between and rotated with a fine pitch around the object to examine. The radiation source emits an X-ray. The emitted X-ray is absorbed and attenuated by the object in part while passing through the object and then reaches the detector.
The intensities of the X-ray detected in rotation directions are expressed by a large number of images captured in those directions. Those images are subject to the filtered back projection based on the Radon transform (see Non Patent Literature 1) to obtain an image of the object cut in any cross-section.
A volume presenting the profile of the object in a three-dimensional space can be reconstructed by arranging the cross-sectional images. A three-dimensional volume can be expressed by a set of voxel values as a two-dimensional image can be expressed by a set of pixel values.
As described above, the reconstruction by tomography techniques is intended to reproduce the original three-dimensional figure of an object as much as possible from images of the object captured in multiple imaging directions. The obtained volume is nothing but an estimated one.
Some tomography techniques can work with visible light, other than the X-ray. Furthermore, the radiation source can be a point source or linear source. It is also possible to eliminate the radiation source and detect light emitted by the object itself with a detector to capture an image of the object in each direction.
The CT scan reconstructs a volume of an object from images captured in a number of imaging directions that rotate about the rotation axis with a fine pitch. Another proposed technique reconstructs a volume of an object by the method of least squares from a number of images of the object captured simultaneously in a number of imaging direction (see Non Patent Literature 2). The technique disclosed in the Non Patent Literature 2 reconstructs a volume of flames from images captured in a number of directions.
As described above, the tomography is used to reconstruct a volume of an object from images of the object captured in multiple imaging directions. The tomography can be considered to be a technique to obtain a most likely (maximum likelihood) volume by minimizing the difference between:
1) images of an object captured in multiple imaging directions; and
2) images of a volume to be reconstructed and seen in the multiple imaging directions.
Additionally, as a correction scheme for making uniform the texture of an object depicted in multiple images, a technique utilizing a steerable pyramid and histogram matching has been proposed (see Non Patent Literature 3).